My wood framed window frames are rotted beyond repair, so I need to replace them.
Aluminium is the choice.
The situation is 100 X 50 wood stud wall, fibre cement clad o/side, plasterboard i/side.

The replacement windows will be Dowell (Boral) which are designed, I think, to be fitted by using ali angle (like angle iron) on the inside, and frame flush to the outside edge of the stud. Frame gets pop riveted to the angle iron?

The existing wood windows are substantially smaller than the opening into which they are fitted, and are spaced with bits of wood where they are nailed to the studs, to roughly centre and square them in the openings.

Question 1. Should I fix the ali angle iron directly to the studs, or build a more precise wood frame, which would then be fitted in the opening, creating hopefully a true rectangle opening of dressed timber, into which an appropriate sized ali window can be fitted?

Question 2. If I fit directly to the studs, should I order the windows a bit bigger than the existing ones to reduce the substantial gaps (15-20mm) around the edges?

Question 3. The outside bottom edge of the bottom (sill?) of the ali frame has to sit on the timber, which means that rain will run onto the timber. There will also be a gap of some sort between the bottom of the ali frame and the wooden opening (may be 10mm or so), and I cannot see a simple solution to making it watertight, unless I use a flashing of some sort, in which case there seems no way to cover it without impeding the water flow.

Any help appreciated.


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